Tagged: shielding

Low Cost Shielding Idea for Plastic RTL-SDRs

Generic RTL-SDRs that come with a plastic enclosure can be prone to picking up interference directly via the PCB itself. Higher end RTL-SDRs generally come with a metal enclosure.

Thanks to Alan R. for submitting a low cost idea he's come up with for shielding his plastic RTL-SDR dongles. Alan writes:

I’ve used this attached method with quite a bit of success for shielding the RTL dongle. It’s just a fizzy orange tube with two holes drilled at each end and some sticky metal insulating tape, which can be bought at any DIY store. Once the USB adapter and RTL dongle are inside they fit snuggly and any standard printer cable with reasonable length works well. Usually this allows for shorter coax connections which again helps keep the signal to noise level reasonable. I opted for a USB with a ferrite core at either end and I also added one to the coax - just because.

If you leave the antenna detached and tune in to any FM radio station you get a strong signal, and as soon as you put the RTL-SDR inside the insulated tube the signal stops. Needless to say if you plug the antenna in then the FM radio comes through with a strong signal. It certainly helps cut down a lot of FM broadcast noise (cheaply!)

I’m not using any band stop / band pass / pre amps and currently I’m receiving loud and clear satellite transmissions - NOAA / Meteor 2. I can even grab the telemetry from AO-73 Funcube with no problems. As the USB is shielded too and is away from the computer it also helps. Plugging the dongle directly into the computer tends to pick up a lot of unwanted noise.

The only thing to watch is it can get a little hot, so some common sense when using it (especially on a hot day). The other advantage is the weather proofing should you get caught in rain!

 

Shielding the SDRplay RSP with Copper Tape

The SDRplay RSP is a $149 USD software defined radio that many consider as a next step upgrade from the RTL-SDR. See our recent review for a comparison between the Airspy, SDRplay RSP and HackRF.

One problem with the SDRplay RSP is that it comes in an unshielded plastic enclosure. This means that strong interfering signals can pass through the enclosure and cause interference, making any filtering done on the antenna less effective. Recently Tom Naumovski wrote in to us to let us know that he has been experimenting with a simple fix that involves shielding his RSP with adhesive copper tape. (Tom carefully notes that doing this may void the warranty). Tom simply wraps the plastic enclosure with conductive copper tape, making sure that electrical contact is made between the copper shielding and RSP ground (e.g. making sure the RSP USB and SMA ports make electrical contact with the copper tape)

Copper tape shielding for the RSP.
Copper tape shielding for the RSP.

After shielding the RSP, Tom tested the shielding effectiveness by using his shielded RSP with no antenna connected to try and pick up an interfering tone transmitted by his HackRF SDR. He collected the results in a pdf file. The results clearly show that the shielded RSP does not pick up, or significantly reduces the power of the HackRF’s interfering tone.

If you want to try this yourself, Tom writes that this copper slug barrier tape found on eBay is the tape he used. Tom also points out the discussion on the Facebook SDRplay group thread he posted where other users have been using aluminium tape or alternative copper tape products.

We note that this same shielding technique can also be used to improve unshielded RTL-SDR dongles.

Enclosing two RTL-SDRs in a metal box to reduce noise

Over on his blog, Twitch has uploaded a post showing how he mounted two RTL-SDR dongles into a single metal case in order to reduce noise. Twitch used a $2 aluminium metal case that he obtained from a local surplus shop and cut it down to size and added holes for switches and BNC plugs. He then mounted two RTL-SDR dongles in the case and used two MCX -> BNC pigtails to get a case mounted coax connector.

He also removed the USB plugs on the RTL-SDR’s and wired them into a USB B plug mounted to the case, making sure to wind the USB power cables through several turns of ferrite core in order to reduce USB noise. Finally he also added a power switch to the USB connections, to be able to easily power off the units when not in use.

rtl_sdr_case
The two RTL-SDR’s placed into a aluminium case.

Installing and Testing the Optional RF Shield on the HackRF

Over on YouTube user Cameron Conover has uploaded a video where he tests the effectiveness of the optional HackRF RF shield and also shows how to install it. The shield solders on to the RF front end of the HackRF and is intended to block signals from entering the device other than through the antenna.

To test the effectiveness of the shield Cameron uses a signal generator to transmit a test signal at 406 MHz. He shows that without the shield in place the HackRF with a 50 Ohm terminator on the antenna input strongly picks up the test signal. After soldering in the shield and testing again, the test signal can no longer be picked up.

HackRF One optional RF shield Installation

Screening Mods for the Airspy

The programmer of Linrad, Leif (sm5bsz) has recently been experimenting with some modifications to the Airspy metal case. He discovered that the USB and RF input connections on the Airspy were not making good electrical connections to the metal case because of the paint on the case. These bad connections caused interfering broadcast FM to be received by the Airspy through the USB cable even when the antenna input was terminated with a dummy load. By sanding down the paint on the metal box to improve the connection he was able to significantly reduce the interference. He writes:

It is a good idea to make sure that both the SMA connector and the USB screen have a good electrical contact with the box. Grounding only the USB screen causes a severe degradation of the NF.

The findings here may also be useful for improving shielded RTL-SDR dongles.


Updates to Shielding the RTL-SDR with an Aluminium Case

A few weeks ago we posted about will1384 who had bought an aluminium case from Ebay and was using it to shield his RTL-SDR. After running multiple tests, will1384 discovered that the aluminium case was actually not helping with shielding performance at all. Oddly his results showed that the aluminium case was actually increasing the amount of noise received. Will has been updating his imgur album with noise analysis results from rtl_power scans over the entire spectrum.

In his latest tests he tried a metal outlet box as the case and saw improved results over the aluminium case. His conclusions seem to indicate that the aluminium box is not a good EMI shield. We’re not sure why he found these results, but one theory might be that because the aluminium case is anodized, it has a non-conductive surface, which might cause poor grounding.

RTL-SDR in a Metal Outlet Box
RTL-SDR in a Metal Outlet Box

Simple RTL-SDR Shielding with Copper Tape

Last month we posted about an RTL-SDR experimenter who shielded his RTL-SDR dongle using an aluminium case. Shielding the RTL-SDR helps to reduce out of band interference which can enter the device through the PCB itself.

Now Melih, another RTL-SDR experimenter has recently posted on his blog about his simpler shielding method that uses cheap copper tape. The copper tape was purchased from ebay, and is the type that is commonly used for creating a slug barrier in the garden.

Over on the Reddit thread discussing his work, there are some concerns about excessive crystal drift due to there being no ventilation holes. However, it seems that the general consensus is that lack of ventilation will not significantly affect crystal drift and may actually help to stabilise the crystal over time by keeping the internal temperature more constant.

You may also be interested in Melih’s previous post where he replaces the MCX connector on the dongle with an SMA female connector.

Copper Tape Shielding RTL-SDR
Copper Tape Shielding RTL-SDR

Shielding the RTL-SDR

Over on Reddit user will1384 has posted about his imgur photo album that clearly documents some well researched steps that he took in an effort to shield the RTL-SDR dongle from interference. Interference is caused by strong out of band signals that can sometimes show up even when no antenna is connected to the dongle. Shielding the dongle helps to remove this interference.

The main steps he took were the following:

  1. Buy an aluminium case from ebay and put the dongle inside it.
  2. Remove the USB connector and ground the dongle ground to the aluminium casing using a 1M Ohm resistor and a 47nf ceramic disk capacitor.
  3. Connect the USB data lines to a USB extension cable and wrap a toroid around the 5v and GND lines and twist the two data lines together.

There is a discussion about this shielding project on Reddit.

Shielding Wiring Diagram
Shielding Wiring Diagram